Mobile radio systems encounter amplitude and phase fluctuations associated with the mobile radio channel. Consider the complex envelope representation of a transmitted signal EQU s(t)=p +m.sub.1 (t)+m.sub.2 (t)+j{m.sub.2 (t)-m.sub.1 (t)},
where p is the pilot tone at channel center (i.e., DC in the case of complex baseband representation), m.sub.1 (t) and m.sub.2 (t) are the upper and lower sideband messages, respectively, and m denotes the Hilbert transform of m. The mobile radio channel imposes distortion on the transmitted signal--most notably, Rayleigh fading, which can be modeled as a multiplicative random process EQU r(t)=A(t)e.sup.j.THETA.(t) s(t)=pA(t)e.sup.j.THETA.(t) +A(t)e.sup.j.THETA.(t) (m.sub.1 (t)+m.sub.2 (t)+j{m.sub.2 (t)-m.sub.1 (t)} )
where A(t) is a Rayleigh-distributed envelope process and .THETA.(t) is a uniformly-distributed phase shift. This distortion imposes difficulties in recovering the message information contained in the transmitted signal and should be removed or compensated for best results.
Prior art techniques for compensating for channel distortion have required an undesirably large amount of memory storage and processing power to achieve sufficient accuracy of compensation. This has resulted in increased receiver cost and higher than necessary power consumption--an undesirable characteristic in battery powered devices, such as portable selective call receivers.
Thus, what is needed is a method and apparatus in a communication receiver for compensating for channel amplitude and phase distortion. The method and apparatus preferably will operate in a manner that maximizes computational accuracy while minimizing memory storage requirements and processing power.